(a) Technical Field
The present invention relates to an apparatus and a method for controlling an engine stop of a hybrid vehicle, more particularly, to an apparatus and a method for controlling an engine stop of a hybrid vehicle configured to quickly avoid a vibration occurring through a resonance region of an engine and to charge a battery while generating a negative torque, when the negative torque is generated using a hybrid starter generator which is connected to the engine side so as to lower rpm of the engine.
(b) Description of the Related Art
A hybrid vehicle is a vehicle that uses an engine and a motor as power sources to improve fuel efficiency, and is configured to include the engine, a driving motor, a battery, and a control unit. The hybrid vehicle includes an inverter for operating these elements, and a hybrid starter generator connected to a crank pulley of the engine in series with the engine, a motor pulley, and a belt. In the case of a generator connected to the motor pulley of the engine in series, it typically includes a hybrid starter generator, and the torque generated by the hybrid starter generator is capable of charging the battery via an inverter.
A control unit of the hybrid vehicle includes an engine control unit (ECU) that controls the engine, a motor control unit (MCU) that controls the hybrid starter generator, a transmission control unit (TCU), and a battery management system (BMS) that manages the state of the battery. The control unit further includes a hybrid control unit (HCU) that performs overall control of the respective control units mentioned above.
A main driving mode of a hybrid vehicle based on such a configuration includes, as is well known, an EV (electric vehicle) mode as a pure electric vehicle mode using only the motor power, a HEV (hybrid electric vehicle) mode as an auxiliary mode using the rotational force of the motor as auxiliary power, while using the rotational force of the engine as the main power, and a regenerative braking (RB) mode that recovers the braking and inertial energy of the vehicle during driving of the vehicle by the braking and inertia of the vehicle through the electric generation in the motor to charge the battery.
In particular, a hybrid vehicle has an idle stop (which is a function of stopping the engine during idling when the vehicle is stopped to improve the fuel economy) so as to improve fuel economy and exhaust performance. The idle stop mode refers to a process of improving the fuel economy and/or exhaust performance by preventing unnecessary engine idling, as one of several techniques for improving the fuel economy and/or exhaust performance of the hybrid vehicle.
The operation and entry of the idle stop mode are processes of forcibly stopping the engine, which has a rotation speed measured in revolutions per minute, such that when the engine is stopped it passes through a resonance region of the engine. Further, when performing a frequent engine stop, it is important to reduce the vibration generated in the engine resonance region.
As a related art, Japanese Patent Publication No. 2013-112265 discloses a technique for generating a negative torque in a traveling hybrid starter generator during automatic stop of the engine, and discloses an apparatus for controlling an engine stop of a hybrid vehicle that performs feedback control depending on the rotational speed profile of the hybrid starter generator that has been set in advance when the engine is automatically stopped.
However, as described above, when performing the control for avoiding an engine resonance region by setting the constant rotation speed, the charging energy of torque generated in the engine is not considered, and there is a problem in terms of fuel efficiency.
Further, upon performing the engine stop, depending on the constant rotational speed of the hybrid starter generator, it is difficult to perform the rapid avoidance of the resonance region when the engine is stopped, and there is a need for operation control of the hybrid starter generator in accordance with the high-efficiency torque of the hybrid starter generator.
FIG. 1 (RELATED ART) shows an operating point of a hybrid starter generator which is connected to an engine when the engine of the hybrid vehicle is stopped, according to the related art.
As shown in FIG. 1, according to the related art, feedback control for following the target speed of the hybrid starter generator is performed when the engine of the hybrid vehicle is stopped, which generates a low negative torque. Thus, when setting the following speed of the hybrid starter generator and executing the feedback control to reach the speed, there is a problem of losing the charging energy of the battery which is generated from the torque of the hybrid starter generator.
Also, in the case of executing the feedback control for following the target speed of the hybrid starter generator when the engine is stopped, there is a problem in which the vibration of the vehicle is generated by quickly avoiding the engine resonance region.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.